The root cause is that tomcat is missing the iXp variables.
You can find back in the tomcat8-stderr file following lines
2019-04-03 12:46:25 Commons Daemon procrun stdout initialized
iXp:ixp.home = null
iXp:ixp.version = 126.96.36.19915
After installation of Tomcat8 , you should have an option 'Configure Tomcat'.
Before doing this, you can check if you find this option under 'start' - programs.
If so, be sure that this is the one for tomcat8 and not the one for tomcat7.
We can workaround with the actual tomcat8 installation you have.
Open a command prompt and go to installation directory of tomcat8/bin directory.
Run following command
tomcat8w //ES /Tomcat8
This will popup window called 'Apache Tomcat 8.5 Tomcat8 Properties'.
Select the 'Java' button.
And add following 3 lines at the bottom in the 'Java Options'.
Fill in correct path for ixp. Example: C:\CA\IXP
Press 'Apply' and close the window
Restart the tomcat8 service.